1. Field of the Invention
The present invention relates to flexible insulating cover structures, and, more particularly, to a detachable insulating cover assembly which is adapted for use in connection with greenhouses and similar structures, having large surfaces which are to be covered with removable low cost insulating sheets, in order to reduce convective heat loss to the outside of the structure.
2. Description of the Prior Art
It is known that convective heat loss through the walls of a structure, especially a light structure such as a greenhouse, can be greatly reduced through the attachment of inexpensive insulating cover sheets of transparent plastic material to the inside of the walls. Comparative measurements have revealed energy savings of up to 40 percent. Particularly advantageous for this purpose are so-called bubble sheets which consist of two layers of thin plastic film which enclose between them rows of small air cushions.
In one known application, large surfaces of bubble sheet are simply being bolted to the structural members of a greenhouse, using screws and hold-down washers (as described in the periodical "Zierpflanzenbau", Issue No. 9, Apr. 28, 1976, pp. 315-318).
In my copending U.S. patent application, Ser. No. 835,540, of Sept. 22, 1977, now U.S. Pat. No. 4,174,596 I have disclosed a detachable insulating cover assembly for greenhouses and the like which features a cover sheet of flexible air-impermeable plastic material which is attached to a wall element of the greenhouse by means of a plurality of spaced fastener assemblies which are arranged along a clamping line near the edge of the sheet, a typical fastener assembly consisting of a fastener base which is permanently attached to the wall element, which is a structural member or a glass panel, for example, and a fastener cap which, when attached to the fastener base, clamps the cover sheet to the latter. For this purpose, each fastener base has a pointed stem over which the cover sheet is impaled, prior to attachment of the fastener cap. The edges of each cover sheet are sealed against the greenhouse structure, so that a closed air space is obtained which contains stationary air which serve as an effective barrier to convective heat transfer.
The cover sheets are removable from the greenhouse structure by releasing the fastener caps and by pulling the cover sheet from the stems of the fastener assemblies. However, the fastener bases remain in place, glued to the inside of the window panels.
It has now been found that there are situations, where it is desirable to attach the fastener assemblies to the structural skeleton of the greenhouse in such a way that the fastener bases are likewise removable from the structure. Such an arrangement has to take into consideration the fact that greenhouses of different age, with different structural components, have to be so equipped. For example, in older greenhouses, the glass panels are in most cases held in place by means of sealing putty, their back side being located very closely to the supporting faces of the skeleton members. The latter are in most cases T-bars, the upstanding central web of the T-bar being located between the edges of two adjacent glass panels. Adding to the problem of limited space between the flange portions of the T-bar and the back sides of the glass panels is the problem of the presence of hardened putty in that space, so that, in the past, there existed a general reluctance towards attempts to find a solution to this problem, especially in view of the fact that the temporary attachment of fastener assemblies to a structural member had to be accomplished without drilling holes into the structural member.
One prior art attempt at attaching insulating cover sheets to structural members of a greenhouse involves the use of U-shaped leaf-spring clamps which open to the width of the structural member, and then clamp the lateral side faces of the latter, when released. This type of clamp is basically identical with the binder clip, an item of office hardward which is primarily used as a temporary clamp for a stack of loose-leaves, or the like. One disadvantage of this type of clamp is that it is generally not suitable for regular T-bars, but that it requires special structural profiles with much larger lateral surfaces, in order to provide a reliable sheet clamping action against these surfaces. (The use of such spring clamps has been suggested by Sibco Universal S.A., 92081 Paris, La Defense.)
Another attempt at a solution to this problem is disclosed in German Gebrauchsmuster (Utility Model) No. 78 02 785, which suggests a fastener base in the form of a one-piece, twice refolded leaf spring with claw-like extremities which reach around the longitudinal edges of the T-bar, thereby attaching the clamp to the structural member. To the top portion of the leaf spring is attached a stem for the attachment of a fastener cap. This proposed clamp has the disadvantage of requiring a special tool for its installation and removal. It also presents a problem with respect to the stability of attachment.